Loop Liquid in an Ising-Spin Kondo Lattice Model on a Kagome Lattice

Phase diagram of an Ising-spin Kondo lattice model on a kagome lattice is investigated by a Monte Carlo simulation. We find that the system exhibits a peculiar ferrimagnetic state at a finite temperature, in which each triangle is in a two-up one-down spin configuration but the spin correlation does not develop any superstructure. We call this state the loop liquid, as it is characterized by the emergent degree of freedom, self-avoiding up-spin loops. We elucidate that the system shows phase transitions from the loop liquid to ferrimagnetically ordered states and a crossover to a partially ferromagnetic state by changing the electron density and temperature. These can be viewed as crystallization and cohesion of the loops, respectively. We demonstrate that the loop formation is observed in the optical conductivity as a characteristic resonant peak.